Tag, You're It! Shark Tagging and Tracking Expeditions Explode

CAPE COD, Mass., Aug. 1, 2010 — -- Nearly a dozen great whites were been spotted off the shore of Cape Cod in the last week alone. Swimming has been banned indefinitely on some beaches.

Now the hunt is on for the monstrous sharks.

ABC News went along, as researchers tracked down the great whites this weekend. First, pilots spot the sharks from above, then relay the location to a patrol boat waiting below.

From there, a crew member with a harpoon jabs the menacing species with a satellite tag.

"We insert this dart under the skin, into the dorsal fin of the shark, and the tag archives information about temperature, depth and light levels," said Dr. Gregory Skomal, senior biologist with the Massachusetts Division of Marine Fisheries.

They're hoping to learn more about where the sharks are coming from, and why they're here. Fact is, sharks of all kinds have made their way to northeast beaches this summer, leading to warnings, beach evacuations and scares for swimmers.

On Friday, a dark dorsal fin popped up out of the water in New Jersey. Moments later, a harmless but scream-inducing sand shark swam ashore.

But it's the great whites Skomal and his team are curious about. Those tags will relay crucial data to a satellite, about the predator's migratory path.

"For scientists, the white shark has been extremely elusive in the Atlantic Ocean," Dr. Skomal said. "You've been hard-pressed to find where they occur. It gives us a unique opportunity to finally get some clues as to how this animal lives in this part of the world."

Scientists know the sharks are coming here to feed on the area's exploding population of gray seals.

They rarely attack humans. Except, of course, in the movies; hello, "Jaws."

But authorities are warning swimmers to be on the lookout, just in case.

"We're hoping to tag through the rest of the summer, as long as the sharks remain here," Skomal said. "I see no reason for them to leave until the temperature changes, or some kind of storm hits, maybe a hurricane. We want to get large numbers tagged so we can really piece together what the patterns are in terms of the life history of this animal."

In exactly six months, the tag will pop off the fin, float to the surface and transmit data to a satellite.

Last year, Skomal carried out a similar experiment, tagging five great whites. The project revealed interesting details about how these mysterious creatures travel.

"[They're] moving from northern areas, like Chatham, Mass., to southern areas, like Florida," Skomal said.

Essentially, the sharks are snowbirds, heading to Florida in the winter, then returning to the northeast come summer.

They're drawn to Cape Cod by the exploding gray seal population. The once-endangered mammals have multiplied on this part of the Atlantic coast, and they're a favorite meal for great whites.

"The white shark is well studied in other parts of the world, and there's an ample number of researchers producing really good information. It's really poorly studied where we live here in the Atlantic. And so just by tagging a handful of these, we'll produce an amazing amount of information," he said.

Inserting the Dart Into the Great White Shark

"We insert this dart under the skin, into the dorsal fin of the shark, and the tag archives information about temperature, depth and light levels."

A pilot is up in the air, looking for white sharks. Once he spots the shark, he tells the captain on vessel, Nick Shipralis, where the shark is.

Once we get close to the boat, our professional harpoon tagger will be on the end of a 20-foot "pulpit," and from the pulpit he will place the tag at the base of the shark's dorsal fin. Everything's got to come together for this to work.

"For scientists, the white shark has been extremely elusive in the Atlantic Ocean," Skomal said. "It gives us a unique opportunity to finally get some clues as to how this animal lives in this part of the world.

Biologists expect the sharks to be dining off the coast of Massachusetts for the next couple of months.